Method for the production of a screw, and screw produced according to said method

ABSTRACT

A screw ( 1 ) having a head ( 2 ), a shaft ( 4 ) that includes a thread ( 5 ), and an interior engaging member ( 3 ) in the head is provided. The screw ( 1 ) is produced from an ultra-high strength steel using a cold forming method.

BACKGROUND

The invention relates to a method for the production of a screw, inparticular a screw for indexable inserts, provided with an interiorengaging member and a screw.

The production of screws by way of cold forming of a source material hasbeen known per se in several variants. Problems only arise withhigh-strength source material. Here, it has previously been understoodthat exclusively cutting, i.e. production by way of material removal canbe used. Such a production of screws entails a high expense and istherefore very costly. Those skilled in the art still believe thatbeyond a certain level of strength of the source material, theproduction of screws with an interior engaging member by way of coldforming is impossible, particularly for relatively small screws.

SUMMARY

The object of the present invention is to overcome the prior mindset ofthose skilled in the art and to provide the ability for producing screwswith an interior engaging member made from a high-strength material.

This is attained according to the invention in a method, in whichultrahigh-strength steel is used and in which a screw including theinterior engaging member is produced by cold forming of the sourcematerial.

Through a series of experiments it has been determined that thoseskilled in the art were erroneous in the prior belief, based onseemingly impossible facts, and that it is actually quite possible toproduce screws made from ultrahigh-strength steel using a method of coldforming according to the invention. Such screws have considerably betterstrength characteristics in reference to screws made by cutting due tothe best possible cross-section ratios. In the previously usedproduction method, the wrench socket in the head could only be producedby way of predrilling and subsequently producing the contour of thewrench by way of punching. However, using the production method of coldforming, the contour of the wrench, e.g., a hexagon socket, is producedby way of a cold forming pressing process without any preliminarydrilling. Therefore, the opening in the wrench socket requiresconsiderably less depth than the same result achieved by the priorprocess, which includes predrilling. Therefore, the strength isconsiderably higher at the point of transition from screw head to shaft,because a lot more material thickness remains between the opening forthe wrench socket and the exterior contour. Therefore, the weak spotsthat develop during cutting are avoided.

Accordingly, the best features for accepting strong torque and also forachieving great tensile strength result from a screw, in particular ascrew with an interior engaging member, made from ultrahigh-strengthsteel and produced by way of cold forming and which can be used withindexable inserts.

Although attempts have already been made to produce screws fromultrahigh-strength steel, limits seemed to appear when an interiorengaging member was also produced. The present invention overcomes thebias that was previously held by those skilled in the art.

It is particularly advantageous for such a method and a screw madeaccording to such a method if the source material used is anultrahigh-strength steel with the composition C 0.03, Mo 5.0, Ni 18.5,Co 8.5, Ti 0.6, Al 0.1, moiety Fe. Particularly with such a composition,those skilled in the art previously thought that any production via coldforming would not be possible. The present invention proves theopposite.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features and particular advantages of the invention will beexplained in greater detail in the following description using thedrawings. They show:

FIG. 1 a side view of a screw, shown partially cut open;

FIG. 2 a top view of the head of the screw.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the drawing, an exemplary embodiment of a screw is shown that is usedfor fastening indexable inserts. The measures according to the inventioncan similarly apply to screws used for other purposes, of course. It hasbeen shown particularly in screws, that have to be produced withinnarrow tolerances and are primarily subject to torque and tensilestress, that the screws made by way of cold forming are considerablybetter than screws made by cutting. Due to the fact thatultrahigh-strength steel are the best source material for such screws,such screws were previously made as turned parts, because one skilled inthe art considered the production by way of cold forming being animpossibility.

A screw 1 shown in the drawing, made particularly for fasteningindexable inserts, comprises a head 2 and a shaft 4 provided with athread 5. On the shaft 4, having the diameter D, the thread 5 is rolledwith the exterior diameter D1. The head 2 in the shape of a raisedcountersunk head, has a diameter D3. In the head 2 an interior engagingmember 3 is formed for accepting a drive element. During the productionin the cold forming process only a small indentation 6 is developed atthe bottom of the interior engaging member 3. In the previously knownproduction methods by way of cutting, a bore 7 (shown in dashed lines)had to be made first for producing the interior engaging member 3,formed as deep as necessary, in order to subsequently produce the wrenchsocket in a punching process. Based on the rather different sectionshaving various diameters, a relatively large degree of formation must beconsidered with this being deemed not possible when ultrahigh-strengthsteel was used.

In the method according to the invention used for producing the screw,in particular a screw for indexable inserts, the production occurs byway of cold forming of the source material, with ultrahigh-strengthsteel being used as the source material, which used to be consideredimpossible by the experts. Within the scope of the invention any type ofultrahigh-strength steel can be processed by way of cold forming of thesource material, however, in the present case, however a source materialof an ultrahigh-strength steel with the composition C 0.03, Mo 5.0, Ni18.5, Co 8.5, Ti 0.6, Al 0.1, moiety Fe is considered particularlysuitable.

This invention allows the production of a screw, in particular, a screwfor indexable inserts, which comprises ultrahigh-strength steel and ismade by way of cold forming. Therefore, essential improvements withregard to the strength of the screw are achieved.

The method for producing the screw uses additional processing steps,similar to the ones used in other cold forming methods, for example washcycles, milling processes for chamfering, grinding, thread rolling,finishing, final quality control etc.

1. A method for producing a screw provided with an interior engaging member, comprising: using ultrahigh-strength steel as a source material and cold forming the screw including the interior engaging member from the source material.
 2. A method according to claim 1, wherein the ultrahigh-strength steel has a of composition C 0.03, Mo 5.0, Ni 18.5, Co 8.5, Ti 0.6, Al 0.1, moiety Fe.
 3. A screw, indexable inserts, comprising ultrahigh-strength steel formed with head having an interior engaging member, by way of cold forming.
 4. A screw according to claim 3, wherein the ultrahigh-strength steel has a composition of C 0.03, Mo 5.0, Ni 18.5, Co 8.5, Ti 0.6, Al 0.1, moiety Fe. 